The invention concerns rotary machines for blow-molding containers made of thermoplastic material in which the container is obtained by blow-molding a preform previously produced by injection molding.
More particularly, it concerns machines having at least one blow-molding station in which a mold carrier unit carries a two-impression mold having two mold cavities each of which is intended to receive one preform. In this case the blow-molding station comprises a blow-molding unit provided with two blow-molding nozzles that are movable between a retracted position and a blow-molding position in which the nozzles can inject the fluid under pressure into the preforms in order to blow-mold the containers. To do this, the blow-molding unit is mounted on a frame element of the blow-molding station in such a way that the two nozzles are placed on either side of a central axis of the mold carrier unit, in correspondence with the principal axes of the two blow-molding cavities.
The invention will be more particularly intended to be implemented on rotary machines comprising several blow-molding stations arranged on a rotor driven in continuous rotational movement. These rotary machines make it possible to achieve high rates of production. The design of two-impression machines, in which each blow-molding station can proceed with the simultaneous blow-molding of two containers, makes it possible to increase the production rate even more while decreasing the unit price of the containers thus produced.
However, the containers that can be manufactured with these two-cavity molds are small in volume. Indeed, the size of the two containers is limited by the size of the mold, which in turn is limited by the size of the mold carrier unit. But mold-carrier units that are too large in size can not be loaded on a rotary machine because this would result in excessively increasing the inertia of the machine""s rotor. Thus, in the high-speed rotary machines that are currently known, the maximum volume of the containers that can be produced in a two-impression mold is less than one liter.
As it happens, however, in many cases the products that are sold in such containers, particularly drinks, are sold in containers of different sizes. Thus, a producer may wish to have containers of different formats, but in every case these containers must be produced under the most advantageous conditions.
Nonetheless, until now, in order to produce low cost containers, it was necessary to have two types of machines: one two-impression machine for small-volume containers, and one one-impression machine for larger containers.
In order to remedy this, a purpose of the invention is to propose a new design of a blow-molding machine that makes it possible to produce both types of containers at the lowest cost, the same machine being able to be configured to produce one or two containers per blow-molding station, without requiring excessive modifications of the machine to change over from one type of production to the other.
To accomplish this, the invention proposes a machine of the type previously described, characterized in that the machine can be changed over to a one-impression configuration in which the mold-carrier unit carries a one-impression mold comprising a single mold cavity the axis of which is appreciably the same as the principal axis of the mold-carrier unit, and in that the blow-molding unit has a second mounting position on the frame element in which the first of two nozzles, called the active nozzle, is arranged in correspondence with the principal axis of the only molding cavity of the one-impression mold.
According to other characteristics of the invention:
the blow-molding unit is moved by sliding between its two mounting positions on the frame;
the blow-molding station has means for inhibiting the second nozzle, called the passive nozzle, so that it is isolated from the source of pressurized fluid;
both nozzles are fed by pressurized fluid from a common source through a distributor that is incorporated into the blow-molding unit, and the distributor has means for isolating the passive nozzle from the source of pressurized fluid;
the nozzles are movable with respect to the blow-molding unit between a retracted position and a blow-molding position, and in the one-impression configuration the second nozzle, called the passive nozzle, is immobilized in a retracted position;
during the blow-molding, each preform is drawn with a drawing rod which is axially engaged inside the preform, through the respective blow-molding nozzle; the blow-molding station has a drawing carriage that is guided axially on the frame element; the carriage has a first and second mounting location each intended to receive a drawing rod when the machine is in the two-impression configuration, and a third mounting location that is used exclusively to receive a drawing rod when the machine is in the one-impression configuration, said location being aligned with the principal axis of the mold carrier unit.